The U.S. and Mexican governments are close to signing a landmark Colorado River deal that will establish rules for sharing water over the next decade and lay out cooperative efforts intended to head off severe shortages.

Mexican and American officials have scheduled a signing ceremony on Sept. 26 in Ciudad Juárez, officials at California water districts said this week. They said that formal event will be followed by a ceremonial signing in Santa Fe, New Mexico, on Sept. 27 attended by representatives from U.S. states.

“This is important to both countries, and will now allow the states and our federal partners to refocus back to drought contingency planning,” said Bart Fisher, chair of California’s Colorado River Board.

California water suppliers – including the Metropolitan Water District of Southern California, the Imperial Irrigation District and the Coachella Valley Water District – approved related agreements on Tuesday, taking some of the final steps necessary to complete the deal. California’s Colorado River Board also signed off at a meeting on Wednesday.

The new accord – titled Minute No. 323 to the 1944 Mexican Water Treaty – outlines a series of measures that build on the countries’ current 5-year agreement, which expires at the end of this year.

The deal will extend provisions in the current agreement, known as Minute 319, that specify reductions in water deliveries during a shortage, as well as increases in water deliveries during wet periods. The agreement also provides for Mexico to continue storing water in Lake Mead, near Las Vegas, helping to boost the reservoir’s levels, which in the past few years have dropped to record lows.

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Lake Mead is the country's largest reservoir. California, Arizona and Nevada have been negotiating a proposed plan to take less water from the reservoir to avert severe shortages.(Photo: Jay Calderon/The Desert Sun)

A final version of the agreement has not yet been released. But according to a summary released by the U.S. Bureau of Reclamation, the agreement will establish a “binational water scarcity contingency plan,” in which Mexico will join U.S. states in temporarily taking less water out of Lake Mead to reduce the risks of the reservoir reaching critical levels.

Those commitments by Mexico would only take effect if California, Arizona and Nevada finish their own Drought Contingency Plan, under which the states would forgo larger amounts of water than they’ve previously agreed to as Lake Mead’s level declines.

The U.S. government has yet to announce details of the upcoming signing ceremony.

“We are very, very close,” said Lori Kuczmanski, a public affairs officer at the U.S. International Boundary and Water Commission in El Paso. “The signing date is not yet confirmed because we don’t have all the domestic approvals that we need. I expect that within the next week we will have that information and we can move forward.”

The agreement reflects the nations’ need to cooperate on water even as tensions remain over President Donald Trump's immigration policies and his plans for building a new wall along the border.

The Colorado River and its tributaries provide water for about 40 million people and more than 5 million acres of farmland.

The legal framework that divvies up the Colorado River was established during wetter times nearly a century ago, starting with the 1922 Colorado River Compact. That and subsequent agreements have handed out more water than what flows in the river in an average year, leading to chronic overuse.

On top of that mismatch between supply and demand, the river has dwindled during a 17-year drought. Climate change is adding to the strains on the river, and scientists have projected warming will likely cause the river’s flow to decrease by 35 percent or more this century.

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Water from the Colorado River rushes into a groundwater recharge facility near Palm Springs, Calif., Wed. July, 5, 2017.(Photo: Zoe Meyers/The Desert Sun)

Talks on the U.S.-Mexico agreement began during President Barack Obama’s administration and have continued with negotiating sessions convened on both sides of the border by the International Boundary and Water Commission, which includes representatives of both governments.

To complete the deal, U.S. water agencies and states needed to sign off on agreements including a U.S.-funded program to invest $31.5 million in water conservation projects in Mexico. Those projects will include infrastructure upgrades such as concrete lining for leaky canals and other improvements to reduce water losses from distribution systems.

The federal government will provide $16.5 million, while the remaining $15 million will come from four water agencies, including the Imperial Irrigation District, the Metropolitan Water District, the Southern Nevada Water Authority and the Central Arizona Water Conservation District.

Each of the water agencies will contribute part of the funding. In return, they will receive a portion of the water freed up through conservation in Mexico.

The conservation projects are intended to generate a total of 229,000 acre-feet of water – enough to cover an area two-thirds the size of Los Angeles with a foot of water. Of that, 50,000 acre-feet will be used to give a boost to the Colorado River system and 70,000 acre-feet will be used to “satisfy the U.S. commitment to provide water for the environment.”

After the U.S. water districts receive the remainder of that water, Mexico will be able to use the additional water supplies made available through the conservation projects.

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The Colorado River flows near Arches National Park in Utah in February 2016.(Photo: Jay Calderon/The Desert Sun)

The Imperial Irrigation District’s board approved seven agreements related to the U.S.-Mexico deal on Tuesday. The district holds the biggest single water entitlement along the Colorado River and supplies water to farms producing crops from alfalfa to Brussels sprouts.

IID Water Department Manager Tina Shields said there’s an interest on both sides of the border in “continuing the cooperative measures outlined in this agreement.”

“This allows for the continued operation of the river system as a basin partnership, and provides benefits to both countries’ water users by more specifically defining reservoir management strategies during this historic drought,” Shields said in a statement. “This leads to a higher level of operational certainty, particularly for lower basin water users that rely upon water deliveries released from Lake Mead.”

The agreement, which will remain in effect through 2026, lays out a strategy for Mexico and the U.S. states to jointly put the brakes on water use to reduce the risks of a crash in the system if the drought persists.

As of this week, Lake Mead stands at just 39 percent full, with its level at an elevation of 1,081 feet.

Under federal guidelines, the Interior Department would declare a shortage – which would trigger cutbacks for Arizona and Nevada – if Lake Mead’s level is projected to be below 1,075 feet as of the start of the following year.

Earlier this year, the Bureau of Reclamation estimated the odds of Lake Mead hitting shortage levels in 2019 at 31 percent. A previous projection had put the odds at 50-50 before last winter brought an above-average snowpack across the Rocky Mountains.

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The marina at Callville Bay has been moved repeatedly as the level of Lake Mead has dropped. This photo was taken in 2014 near the marina’s administration building, where the water level stood when the reservoir was nearly full in 2000.(Photo: Richard Lui/The Desert Sun)

The treaties that originally divided the river among seven states and Mexico allocated 7.5 million acre-feet of water per year for states in the river’s upper basin, including Colorado, Wyoming, Utah and New Mexico; 7.5 million acre-feet for the lower basin states of Nevada, Arizona and California; and 1.5 million acre-feet for Mexico.

A series of negotiated agreements between Mexico and the U.S. have been tacked on as amendments to the countries’ 1944 treaty, and those deals are formally known as minutes – a reference to the minutes of diplomatic meetings where the agreements are reached.

For decades, so much water has been diverted from dams all along the Colorado that the river seldom meets the sea. The river’s delta in Mexico has become a dusty stretch of desert.

Mexico diverts its share of the river from the Morelos Dam to sustain desert cities and the farmlands of the Mexicali Valley.

Under the agreement, Mexico, the U.S., and nongovernmental organizations will team up to secure water for wetlands south of the border, plus $18 million for habitat restoration and monitoring.

The federal government’s summary of Minute 323 says the two countries “share a common vision on a clear need for continued and additional actions to reduce the risk of reaching critical reservoir elevations at Lake Mead.”

The document details how continued declines at the reservoir would trigger a rising scale of cutbacks in water deliveries, with Mexico contributing alongside the states – as long as the states have a similar plan in place.

Last year, water managers in California, Arizona and Nevada had expressed hope they would soon finish negotiating their plan to collectively take less water out of Lake Mead during drought. But that agreement hasn’t been finalized, and one sticking point has been California’s long-delayed efforts to cope with the deterioration of the Salton Sea, which is sustained by Colorado River water.

Until recently, IID had warned that it wouldn’t take part in the proposed deal until the state presents a credible “road map” to restore deteriorating shoreline habitats and cover up growing stretches of dust-spewing lakebed around the shrinking lake.

Within the past month, though, IID and two other local agencies negotiated an agreement with Gov. Jerry Brown’s administration that would commit state officials to following through on their pledges at the Salton Sea over the next decade.

That proposed Salton Sea deal sets annual targets for California agencies to build thousands of acres of ponds, wetlands and other dust-control projects around the lake as its shorelines retreat over the next 10 years. The lake is about to start shrinking rapidly next year as more water is transferred from the Imperial Valley to growing cities in Southern California.

If the proposed Salton Sea agreement is approved by California’s State Water Resources Control Board, it would finally help clear the way for the larger three-state agreement, and it would become one more piece in an interconnected web of deals – all of them focused on strategies for coping with less water as the Colorado River dwindles.